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THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

PRESENTED  BY 

PROF.  CHARLES  A.  KOFOID  AND 
MRS.  PRUDENCE  W.  KOFOID 


Hr 


UNIVERSITY    OF    CALIFORNIA    PUBLICATIONS 

Wt 
ZOOLOGY 

6,  No.  13,  pp.  285-312  December  28,  1910 


SIGNIFICANCE  OF  WHITE  MARKINGS 

IN 

BIRDS  OF  THE  ORDER  PASSERIFORMES 


BY 

HENRY  CHESTER   TRACY 


BERKELEY 

THE   UNIVERSITY  PRESS 


UNIVERSITY    OF    CALIFORNIA    PUBLICATIONS 

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OTTO    HAEEASSOWITZ  E.   PEIEDLAENDEE   &   SOHN 

LEIPZIG  BEELIN 

Agent  for  the  series  in  American  Arch-  Agent  for  the  series  in  American  Arch- 
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Psychology.  ogy,  and  Memoirs. 

ZOOLOGY. — W.  E.  Eitter  and  C.  A.  Kofoid,  Editors.  Price  per  volume  $3.50.  Commenc- 
ing with  Volume  II,  this  series  contains  Contributions  from  the  Labora- 
tory of  the  Marine  Biological  Association  of  San  Diego. 

Cited  as  Univ.  Calif.  Publ.  Zool. 
Vol.  1.    1.  The  Hydroida  of  the  Pacific  Coast  of  North  America,  by  Harry  Beal 

Torrey.    Pp.   1-104;   plates  1-11.    November,   1902 $1.00 

2.  A  Case  of  Physiological  Polarization  in  the  Ascidian  Heart,  by  Frank 

W.  Bancroft  and  C.  O.  Esterly.    Pp.  105-114.    April,  1903 10 

3.  Embryology  and  Embryonic  Fission  in  the  Genus    Crisia,    by    Alice 

Eobertson.    Pp.  115-156,  plates  12-15.    June,  1903 .60 

4.  Correlated  Protective  Devices   in   some   California  Salamanders,   by 

Marion  E.  Hubbard.    Pp.  157-170,  plate  16.    November,   1903 » 

5.  Studies  on  the  Ecology,  Morphology  and  Speciology  of  the  Young  of 

some  Enteropneusta  of  Western  North  America,  by  William  E.  Eitter 

and  B.  M.  Davis.    Pp.  171-210,  plates  17-19.    February,  1904 .50 

6.  Eegeneration   and   Non-Sexual   Eeproduetion   in   Sagartia   davisi,   by 

Harry  Beal  Torrey  and  Janet  Euth   Mery.    Pp.   211-226,   7  text- 
figures.    May,  1904  L 15 

7.  The  Structure  and  Eegeneration  of  the  Poison  Glands  of  Plethodon,  by 

C.  O.  Esterly.    Pp.  227-268,  plates  20-23.    June,  1904 1.00 

8.  The  Distribution  of  the  Sense-organs  in  Microscolex  elegans,  by  John 

F.  Bovard.     Pp.  268-286,  plates  24-25.     December,  1904..... .60 

9.  Some  New  Tintinnidae  from  the  Plankton  of  the  San  Diego  Region, 

by  Charles  A.  Kofoid.    Pp.  287-306,  plates  26-28.    July,  1905 25 

Index,  pp.  307-317. 
Vol.  2,    (Contributions  from  the  Laboratory  of  the  Marine  Biological  Association 

of  San  Diego.) 

Introduction.  A  General  Statement  of  the  Ideas  and  the  Present  Aims 
and  Status  of  the  Marine  Biological  Association  of  San  Diego,  by 
William  E.  Bitter,  Director  of  the  Station.  Pp.  i-xvii.  2  Maps  .25 

1.  The  Hydroids  of  the  San  Diego  Eegion,  by  Harry  Beal  Torrey.    Pp. 

1-43.    22  text  figures.    December,  1904. 

2.  The  Ctenophores  of  the  San  Diego  Eegion,  by  Harry  Beal  Torrey. 

Pp.  45-51,  plate  1.    December,  1904. 

Nos.  1  and  2  in  one  cover 60 

3.  The  Pelagic  Tunicata  of  the  San  Diego  Eegion,  excepting  the  Larvacea, 

by  William  E.  Eitter.    Pp.  61-112,  plates  2-3.    31  text-figures.  Jan- 
uary,   1905    65 

4.  The  Pelagic  Copepoda  of  the  San  Diego  Eegion,  by  C.  O.  Esterly.    Pp. 

113-233,  62  text  figures.    September,  1905 1.25 

6.  The  Non-encrusting  Chilostomatous  Bryozoa  of  the  West  Coast  of  North 
America,  by  Alice  Eobertson.  Pp.  235-322,  plates  4-16.  December, 
1905 _ 1.00 

6.  Differentiation  in  Hydroid  Colonies  and  the  Problem  of  Senescence, 

by  Harry  Beal  Torrey.    Pp.  232-332,  4  text-figures.    December,  1905. 

7.  The  Behavior  of  Corymorpha,  by  Harry  Beal  Torrey.    Pp.  333-340, 

6  text-figures. 

Nos.  6  and  7  in  one  cover 25 

8.  Dinoflagellata  of  the  San  Diego  Eegion.    I.  On  Heterodinium,  a  New 

Genus  of  the  Peridinidae,  by  Charles  Atwood  Kofoid.    Pp.  341-368, 

plates  17-19.    January,  1906  „ 25 

Index,  pp.  369-382. 


*  Supply  limited;  sold  only  with  complete  volumes. 


UNIVERSITY    OF    CALIFORNIA    PUBLICATIONS 

IN 

ZOOLOGY 

Vol.  6,  No.  13,  pp.  285-312  December  28,  1910 


SIGNIFICANCE  OF  WHITE  MARKINGS 

IN 

BIRDS   OF   THE   OEDER   PASSERIFORMES.* 

BY 

HENRY    CHESTER    TRACY. 


CONTENTS. 

PAGE 

Introduction    285 

Intrinsic  Factors  in  the  Evolution  of  Color 286 

White  Markings  as  Visual  Clues 289 

The  Problem  Discussed  for  Birds  of  the  Open 295 

The  Problem  Discussed  for  Arboreal  Species 297 

Special  Study  of  the  Mniotiltidae 305 

Sexual  Selection  as  Affecting  White  Patterns 308 

Directive  Markings  Outside  the  Order  Passeriformes 309 

Conclusion    309 

INTRODUCTION. 

The  present  investigation  was  undertaken  for  the  purpose 
of  testing  the  validity  of  one  of  the  earliest  recognized  categories 
of  coloration,  that  of  ''Directive  Markings,"  in  a  single  order 
of  birds.  The  term  directive  is  used  in  the  sense  given  it  by  Tedd 
(1888)  and  not  that  of  later  writers  (Marshall,  1902),  who  have 
used  the  word  as  expressing  a  different  function  of  white 
markings  in  butterflies'  wings — protective  through  drawing  the 
enemy's  attack  away  from  vital  parts.  As  here  used  it  resembles 
the  term  recognition  markings,  and  might  be  regarded  as  a 


*  The  present  paper  is  the  result  of  work  carried  on  in  the  Department 
of  Zoology  of  the  University  of  California  as  partial  fulfillment  of  the 
requirements  for  the  master's  degree,  under  the  direction  of  Professor 
Charles  A.  Kofoid,  to  whom  the  writer  is  indebted  for  advice  and 
criticism.  He  is  also  under  many  obligations  to  Mr.  Joseph  Grinnell,, 
Director  of  the  Museum  of  Vertebrate  Zoology,  for  much  information 
placed  at  his  dsposal.  The  author  also  had  access  to  the  large 
collections  in  the  Museum,  and  was  allowed  free  use  of  these  and  of 
such  data  on  file  there  as  proved  pertinent  to  the  problem  in  hand. 


M370348 


286         University  of  California  Publications  in  Zoology.     ITOL-  6 

synonym  were  there  not  good  reasons  for  believing  that  the 
white  markings  exposed  in  flight  serve  rather  as  a  clue  to  the 
direction  taken  by  disappearing  forms  of  birds,  than  as  an  aid 
to  recognition  of  the  species. 

The  investigation  of  the  theory  of  directive  markings  in  birds 
is  hampered  by  the  impracticability  of  carrying  on  field  experi- 
ments such  as  those  of  Professor  Reighard  (1908)  in  pursuance 
of  a  similar  inquiry  in  regarding  warning  coloration  in  fishes. 
Obviously  it  is  out  of  the  question  to  capture  and  liberate  large 
numbers  of  birds  with  a  view  of  detecting  natural  reactions  under 
such  artificial  conditions.  Field  observations  can,  however,  be 
offered,  but  these,  in  the  nature  of  the  case,  do  not -afford  evidence 
which  is  experimentally  precise.  Much  depends  upon  the  indi- 
vidual in  the  field — the  personal  equation.  This  source  of  error 
cannot  be  set  aside  by  recourse  to  photographs,  for  the  reason 
that  the  crux  of  the  problem  of  directive  markings,  in  so  far  as 
it  concerns  actual  perception,  is  the  effect  of  the  moving  white  of 
the  wings  or  other  parts  of  the  flying  birds.  Photographic  plates 
show  but  the  fixed  effect  of  motionless  patterns,  and  tell  us 
nothing  as  to  their  eificacy  in  attracting  visual  attention  to  those 
patterns  in  motion. 

I  have,  therefore,  narrowed  the  field  to  a  discussion  of  the 
revealing  properties  of  flight-exposed  white  markings,  and  a 
study  of  the  occurrence  of  such  markings  throughout  the  order 
Passeriformes,  deducing  from  such  occurrence  a  very  suggestive 
correspondence  of  coloration  with  habit  and  feeding  range.  I 
have  no  direct  evidence  to  offer  as  to  the  origin  and  mode  of 
evolution  of  the  white  markings  in  birds.  It  may  not  be  amiss, 
however,  before  proceeding  further,  to  call  attention  to  the 
limitations  of  explanations  based  on  intrinsic  factors  alone. 

INTRINSIC  FACTORS  IN  THE  EVOLUTION  OF  COLOR. 

Riddle  (  1908)  has  proved  that  the  melanin  deposited  in 
barbules  varies  with  nutrition.  He  has  also  shown  that  funda- 
mental bars  in  feathers  may  have  their  origin  in  rhythms  of  blood 
pressure.  He  thus  establishes  a  presumption  in  favor  of  a 
continuously  acting  cause,  apart  from  heredity,  governing  the 
degree  of  pigment  deposited  in  birds'  feathers.  He  is  perhaps 


191°]  Tracy:  White  Markings  in  Birds.  287 

right  in  asserting  that  further  evolutionary  studies  of  bird 
coloration  should  take  their  departure  from  this  point.  Neverthe- 
less, if  this  be  true,  the  gap  between  fundamental  bars  in  feathers 
and  the  varied  patterns  in  which  white  appears  in  every  con- 
ceivable combination,  often  accompanied  by  intensification  of 
pigment  deposits  in  adjacent  plumage,  is  one  which  can  only 
be  filled  by  difficult,  expensive,  and  long  continued  research.  In 
the  meantime  the  discoveries  of  Thayer  (1909)  have  greatly 
simplified  the  explanation  from  the  selective  standpoint,  while 
those  of  Reighard  point  to  an  intrinsic  tendency  toward  variety 
of  pattern,  needing  only  immunity  such  as  that  afforded  by  a 
coral  reef,  to  develop  colors  and  contrast  that  are  neither  adaptive 
nor  due  to  sexual  selection,  and  for  which  the  physiological  ele- 
ments of  nutrition,  temperature,  etc.,  do  not  account.  Thus  it  is 
probable  that  the  production  of  bars  and  stripes  in  feathers,  and 
the  rate  of  pigment  deposit,  are  but  secondary  processes  in  a 
larger  scheme.  They  may  themselves  be  dependent  on  selective 
agencies  which,  if  they  exist  at  all,  operate  upon  the  whole 
organism. 

If  we  were  concerned  here  with  the  problem  of  bird  color- 
ation in  general,  we  might  linger  upon  examples  of  an  apparent 
physiological  basis  for  dark  coloration,  such  as  that  of  most 
species  of  Corvidae;  these  are  largely  omnivorous  feeders,  active 
and  of  exuberant  vigor.  But  we  should  certainly  be  wrong  if  we 
failed  to  take  account  of  the  great  degree  of  immunity  which 
these  birds  enjoy  from  the  attacks  of  raptorial  birds,  because  of 
their  size  and  aggressiveness.  It  is  doubtful  whether  a  seed- 
eating  bird  of  delicate  flesh  and  harmless  disposition  could  have 
been  permitted  to  develop  such  a  black  plumage  as  that  of  the 
raven,  even  had  the  physiological  excuse  for  pigment  excretion 
been  as  great  in  its  case.  Some  other  way  would  have  been  found, 
we  may  reasonably  say,  for  the  excretion  of  melanin,  or  else  that 
type  of  bird  would  have  become  extinct  for  lack  of  protective 
coloration. 

Similar  difficulties  involve  such  special  varieties  of  the 
physiological  explanation  of  color  patterns  as  are  connected  with 
color  distribution  on  the  breast,  crown,  rump,  etc.,  of  birds, 
regarded  as  centers  of  high  or  of  deficient  circulation.  A  study 


288         University  of  California  Publications  in  Zoology.     [VOL.  6 

of  any  series  of  birds  ranging  through  half  a  dozen  families  will 
give  quite  contradictory  results.  The  crown  will  be  found  white 
on  some,  black  on  others;  the  breast  usually  light  colored,  but 
sometimes  with  a  spot  or  chain  of  spots,  or  the  throat  spotted  and 
the  breast  plain ;  and  the  rump  white  in  some,  heavily  pigmented 
in  others.  Only  patient  ingenuity  could  long  persist  in  seeking 
evidence  for  the  correlation  of  pigmented  areas  with  regions  of 
fuller  circulation;  and  the  seeker  for  such  evidence  must  shut 
his  eyes  to  the  patent  fact  that  to  produce  a  monochrome  plumage 
such  as  that  of  the  Leconte  thrasher  the  dermal  circulation 
must  be  uniform  over  the  entire  surface  of  the  body ;  the  existence 
of  the  theory  would  seem  to  demand  the  denial  of  such  a  con- 
dition. 

Cunningham's  suggestion  (1900,  p.  109)  of  a  local  stimulus 
incident  to  the  elevation  of  plumes,  etc.,  in  courtship,  is  useful 
in  accounting  for  the  special  development  of  certain  epidermal 
features,  but  it  sheds  no  light  on  the  cause  of  intensification  of 
color  in  the  breeding  male,  in  the  plumage  as  a  whole.  The 
vigor  theory  attempts  to  do  this,  but  leaves  untouched  a  large 
number  of  instances  in  which  there  exists  no  sexual  dimorphism 
in  coloration,  and  still  others  in  whhh  the  female  takes  over  not 
only  the  color  character,  but  also  the  courting  antics  of  the 
male,  leaving  him  the  responsibility  for  incubation,  as  is  the 
case  in  the  knot  (Tringa  canutus). 

The  other  class  of  intrinsic  factors  in  color  evolution  grouped 
under  the  general  term  heredity,  is  one  which  this  paper  will 
merely  recognize  as  existing,  a  potent  but  little  understood  influ- 
ence. If  it  can  be  shown  that  white  markings  do  not  occur 
indiscriminately  on  birds  of  all  habits  and  environments,  but  are 
associated  with  similar  habits  and  ranges  among  birds  not 
otherwise  closely  allied,  it  will  be  clear  that  they  cannot  be 
regarded  solely  as  evidences  of  the  manifestation  of  hereditary 
tendencies,  but  may  fairly  be  attributed,  at  least  in  part,  to 
selective  influences. 

Whatever  the  original  cause  of  pigmentation  or  absence  of 
pigment  and  its  replacement  by  structural  colors,  and  whatever 
the  mode  of  evolution  of  such  colors  and  combinations,  the  as- 
sumption of  a  principle  of  natural  selection  everywhere  efficient 


191°]  Tracy:  White  Markings  in  Birds.  289 

though  sometimes  passive,  is  justified  by  the  facts  as  to  the  dis- 
tribution of  white  patterns  in  passeriform  birds  of  the  United 
States. 

WHITE   MARKINGS  AS   VISUAL   CLUES. 

Coloration  in  birds,  whatever  its  cause  or  the  mechanism  of 
its  production,  is  conceded  to  be  adaptive;  it  responds  to  their 
needs,  forms  a  part  of  their  life  adjustments. 

Concealment  from  its  enemies  is  not  the  only  need  in  a  bird's 
life,  not  the  only  adjustment  that  affects  color-patterns.  The 
bird  also  needs  to  be  made  known  to  other  individuals  of  its 
kind,  and  to  other  species  associated  with  it;  and  this  need  has 
certainly  been  met.  Just  how  it  has  been  met  depends  upon 
the  bird 's  manner  of  life,  and  upon  its  chosen  habitat ;  this  much 
we  know.  Without  entering  upon  any  disputed  phase  of  the 
subject,  we  may  state  at  the  outset  that  the  need  exists  and  has 
been  met,  if  not  by  special  provision  in  coloration,  at  least  by 
peculiarities  of  form  and  manner,  or  by  qualities  of  voice. 

The  vital  importance  to  a  bird  of  seeing  and  being  seen  by 
its  companions,  hardly  finds  a  parallel  among  the  lower  verte- 
brates ;  certainly  not  among  most  fishes,  though  a  school  of  fishes 
bears  a  superficial  resemblance  to  a  flock  of  birds.  Neither  in 
organization  nor  in  instinct  does  the  one  approach  the  high 
development  of  the  other.  A  comparison  of  the  brain  of  a  perch 
with  that  of  a  pigeon  shows  the  remarkable  superiority  of  the 
latter  in  respect  to  cerebral  development.  The  phenomena  of  the 
associations  of  a  bird's  life,  the  well-known  facts  of  mutual  in- 
dependence in  feeding,  nesting  and  migration  among  nearly  all 
of  the  class  Aves,  indicate  the  degree  to  which  individualism 
has  been  subordinated,  and  cooperation  of  a  certain  kind 
developed. 

There  are,  however,  great  differences  within  the  class.  If  we 
are  to  make  any  comparison  between  these  and  the  lower  verte- 
brates, let  it  be  between  gregarious  sea-birds  and  fishes,  not 
between  oscines  and  herring.  Delicate  life-adjustments  are  to 
be  found  among  the  higher  genera  of  the  perching  birds  that  are 
missing  from  the  more  primitive  divers  or  long-winged  swim- 
mers, as  well  as  from  fishes.  The  number  and  variety  of  perils 


290          University  of  California  Publications  in  Zoology.     [VOL.  6 

that  daily  surround  our  smaller  land-birds,  and  the  extent  to 
which  these  may  be  diminished  by  the  birds'  keeping  in  touch 
with  one  another,  point  to  the  need  of  something  more  than 
concealing  coloration,  and  admit  of  special  adaptions  that  shall 
act  in  harmony  with  it  and  yet  serve  to  reveal  the  bird  to  its 
kind. 

Notwithstanding  this  distinction  there  will  be  some  who 
fail  to  find  in  the  life-relations  of  the  Passeriformes  anything 
to  occasion  the  development  of  marks  whose  main  function  shall 
be  that  of  revealing  the  birds  to  each  other.  Thayer  (1900), 
exposing  the  weakness  of  the  "banner-mark  theory,"  indirectly 
implicates  all  theories  of  directive  coloration,  as  well  as  that 
of  warning  colors,  and  has  since  made  them  the  object  of  special 
attack  (A.  H.  Thayer,  1909).  The  ground  for  his  criticism — and 
it  is  a  good  one — is  that  birds,  in  order  to  profit  by  such  aids  as 
signs  and  signals,  or  at  least  to  need  them,  must  be  less  acute 
than  human  observers,  who  easily  recognize  species  of  birds  by 
slight  hints,  such  as  are  afforded  by  silhouette,  by  mode  of  flight, 
by  mannerisms  of  one  sort  or  another,  rather  than  by  special 
marks.  This  is  so  true  that  it  must  and  does  discredit  the  crude 
interpretations  such  as  the  title  "banner-mark"  suggests.  We 
must  distinguish  between  hypothetical  functions,  the  creation 
of  fancy,  and  a  series  of  well-defined  stripes,  bars,  or  checks, 
which  may  be  interpreted  by  any  one  of  at  least  three  categories, 
of  which  that  of  "concealing  coloration"  is  only  one. 

Starting  out  with  a  presumption  in  favor  of  some  form  of 
revealing  clues  among  the  higher  land-birds,  and  eliminating  a 
terminology  which  has  been  misleading,  it  remains  for  us  to 
determine,  if  possible,  what  these  clues  are,  and  whether  color 
features  form  a  part  of  them;  if  so,  how  this  harmonizes  with 
the  function  of  the  same  or  similar  color  features  as  concealing. 

How  do  the  birds  of  our  woods  and  fields  actually  keep  track 
of  one  another?  Obviously  to  a  great  extent  by  vocal  sounds 
which  they  utter  frequently  when  moving  about  in  the  foliage, 
or  in  unison  when  leaving  a  feeding  ground  as  a  flock;  by  call- 
notes,  when  moving  in  pairs  or  companies;  by  location  notes, 
when  separated  and  seeking  to  come  together.  No  one  doubts  the 
existence  of  such  vocal  clues  or  their  vital  necessity  to  birds 
belonging  to  the  order  under  discussion. 


1910]  Tracy:  White  Markings  in  Birds.  291 

There  are  birds  that  appear  to  depend  almost  entirely  upon 
directive  calls  for  keeping  together ;  they  have  become  habituated 
to  feeding  in  close  and  uninterrupted  cover  where  they  see  other 
birds  only  at  close  range,  or  very  seldom  at  any  great  distance. 
Obviously  they  must  keep  within  hearing,  or  be  lost  to  their 
companions.  Sound-clues  are  sufficient  in  their  case.  This  is 
true  of  the  bush-tit  (Psaltriparus  minimus  calif ornicus),  some 
warblers,  and  nearly  all  the  wrens.  These  are  birds  of  plain 
colors,  for  the  most  part,  and  without  white  patterns  of  any  sort. 

Among  arboreal  birds  of  open  feeding  range  that  are  con- 
stantly exposed  to  view,  different  conditions  obtain.  Call-notes 
are  used,  but  glimpses  of  other  birds  in  flight  may  be  just  as 
useful  for  purposes  of  direction,  since  such  glimpses  are 
frequently  to  be  had.  Sight  plays  a  part  of  corresponding 
importance  in  the  economy  of  bird-movement — to  some  extent 
replaces  sound  as  a  means  of  recognition. 

As  there  is  in  the  general  coloration  of  open-ranging  birds  no 
response  to  the  need  of  some  rapid  and  easy  means  of  recog- 
nition, and  as  the  special  color  patterns  that  have  heretofore 
been  regarded  as  serving  that  purpose  are  now  being  claimed  as  a 
part  of  "concealing  coloration"  (A.  H.  Thayer,  1909),  it  might 
appear  that  the  category  of  directive  markings  is  soon  to  lose  its 
status  altogether.  But  general  coloration  is  seen  to  be  normally 
protective,  for  birds  that  need  protection ;  and  as  for  the  special 
patterns,  even  a  satisfactory  demonstration  of  their  "oblit- 
erative ' '  effect  does  not  warrant  the  conclusion  that  such  is  solely 
or  mainly  their  effect  in  all  cases. 

For  a  discussion  of  the  "disruptive  effect  of  color  patterns" 
the  reader  is  referred  to  G.  H.  Thayer,  1909,  pp.  77-79,  and  to 
A.  H.  Thayer,  1909,  pp.  562  et  seq.  The  evidence  here  offered 
of  their  value  as  revealing  characters,  must  not  be  regarded  as 
contradicting  anything  but  the  application  of  the  "concealing" 
principle  to  birds  in  flight. 

During  the  month  of  February  the  writer  had  under  observa- 
tion a  flock  of  fifteen  meadowlarks  (Sturnella  neglecta),  which 
foraged  in  vacant  lots  and  fields  within  the  city  limits  of  Berkeley. 
They  were  well  spaced  while  feeding,  and  when  disturbed  some 


292         University  of  California  Publications  in  Zoology.     ITOL-  6 

would  fly  across  a  road  into  the  neighboring  field,  where  they 
would  presently  be  followed  by  others.  Their  white  tail-borders 
were  often  conspicuous  during  the  entire  flight  of  the  birds,  the 
tail  remaining  partly  spread.  As  the  meadowlarks  on  being 
flushed  rose  to  the  height  of  a  man's  head  or  higher,  they  must 
have  seen  the  retreating  forms  from  a  similar  view-point,  i.e., 
against  a  dark  background.  They  would  not  commonly  see  them 
against  the  sky.  For  the  birds  themselves,  white  tail-borders 
would  serve  no  purpose  if  not  a  directive  one.  Common  observa- 
tion does  not  seem  to  be  at  fault  here,  nor  the  term  ' '  white 
guides"  ill-chosen. 

It  will  be  seen  that  the  common  assumption  to  -the  effect  that 
white  upon  an  object  makes  it  conspicuous  is  well  grounded*  in 
this  case,  for  the  reason  that  there  is  nothing  corresponding  to 
it  in  the  usual  background;  further,  because  it  does  not  in  the 
least  efface  the  outlines  of  the  bird's  contour,  and  finally  because 
the  bird  is  in  motion  at  the  time  when  the  marking  is  displayed. 
We  take  note,  therefore,  of  the  distinction  between  a  flight- 
exposed  marking  and  one  that  appears  at  its  full  value  when  the 
bird  is  at  rest.  The  former  acquires  added  conspicuousness  from 
the  fact  that  a  moving  object  fixes  and  holds  the  attention,  indeed 
a  white  object  moving  across  a  dull  background  is  the  best 
mechanism  that  can  well  be  devised  for  signalling  at  long 
distances. 

Mr.  A.  H.  Thayer,  in  the  article  to  which  we  have  just 
referred,  indicates  a  supposed  correlation  between  white  rear- 
markings  and  the  habit  of  nesting  on  the  ground  and  flying 
from  the  nest  when  disturbed,  stating  that  the  markings  are 
absent  from  birds  that  habitually  run  from  it  to  escape  a  furred 
enemy.  This  would  point  to  an  obliterative  function  in  the  rear- 
mark,  which  shows  white  against  the  sky  as  seen  from  the  level 
of  a  quadruped.  This  statement  and  conclusion  seem  to  have 
been  hastily  made,  for  they  apply  only  in  the  case  of  water  birds 
such  as  rails,  coots  and  gallinules  which  the  author  of  the  state- 
ment had  in  mind.  The  horned  lark  (Otocoris  alpestris,  all 
subspecies),  the  meadowlark  (Sturnella  magna  and  8.  neglecta), 
and  the  vesper  sparrow  (Pooecetes  gramineus),  are  among  the 


191°]  Tracy:  White  Markings  in  Birds.  293 

rear-marked  birds  that  run  from  the  nest,  habitually,  when 
disturbed. 

In  the  foregoing  paragraphs,  the  evidence  for  the  revealing 
function  of  white  rear-markings  exposed  in  flight  has  been  given 
as  common  observation,  supplemented  by  psychological  analysis 
of  the  facts ;  and  the  supposed  instance  of  a  concealing  function 
in  the  case  of  certain  birds  has  been  shown  to  be  quite  incon- 
clusive as  regards  perching  birds.  These  considerations  alone 
would  point  strongly  to  the  other  interpretation  of  the  markings 
as  advanced  by  Todd  (1888),  and  rather  generally  accepted 
since.  They  are  not,  however,  the  only  ones  bearing  on  the 
question. 

In  giving  recognition  to  the  theory  of  directive  markings  of 
this  type  Wallace  (1889,  p.  222)  alluded  to  their  prevalent 
occurrence  among  flocking  birds,  as  strengthening  the  theory, 
since  it  was  just  here  that  they  would  be  of  the  greatest  use.  He 
did  not,  however,  test  the  facts  regarding  such  occurrence,  or 
inquire  into  the  question  of  a  significant  absence  of  white  mark- 
ings among  non-flocking  birds;  nor  has  anyone  else  done  so, 
heretofore.  It  is  a  test  that  is  easily  made  by  segregating  all  the 
birds  bearing  the  white  rear-marks,  and  making  an  inventory  of 
those  that  remain.  In  order  to  judge  of  the  significance  of  the 
resulting  division  it  is  necessary  to  know  to  what  extent  the  birds 
thus  arbitrarily  separated  differ  in  habits,  especially  as  regards 
flocking ;  and  this  is  not  as  easy  as  might  be  supposed,  among  the 
perching  birds. 

The  accompanying  list  gives  all  the  species  of  open-ground 
passeriform  birds  native  to  North  America.  Although  the  white 
tail-borders  occur  also  on  a  few  arboreal  birds,  these  may  be 
regarded  as  coming  in  the  class  of  ' '  top-patterns, ' '  which  will  be 
taken  up  in  connection  with  birds  of  the  forests  and  thickets. 


294         University  of  California  Publications  in  Zoology.     tv°L- 


PASSERIFORM  BIRDS   OF   THE   OPEN. 

WITH    CONCEALED    WHITE. 


ICTERIDAE 

Sturnella  magna 

Sturnella  neglecta 
ALAUDIDAE 

Otocoris  alpestris,  all  subsp. 

Alauda  arvensis 
FRINGILLIDAE 

Calcarius  lapponicus 

Calcarius  pictus 

Calcarius  ornatus 

Bhyncophanes  mccowni 

Pletrophenax  nivalis,  all  subsp. 

Plectrophenax  hyperboreus 

Calamospiza  melanocorys 

Chondestes  grammacus  subsp. 

Pooecetes  gramineus,  2  subsp. 


Junco  hyemalis,  all  subsp. 

Junco  aikeni 

Junco  phaeonotus,  3  subsp. 

Junco  bairdi 

Junco   insularis 

MOTACILLADAE 

Anthus  pratensis 
Anthus  spraguei 
Anthus  cervinus 
Anthus   rubescens 
Budytes  flavus.  alascensis 
Motacilla  alba 
Motacilla  ocularis 
TROGLODYTIDAE 

Heleodytes  brunneicapillus 
Oroscoptes  montanus 


WITHOUT  CONCEALED  WHITE. 


FRINGILLIDAE 

Leucosticte  atrata 
Leucosticte  australis 
Leucosticte  tephrocotis 
Leucosticte  griseonucha 
Passerculus  bairdi 
Passerculus    princeps 
Passerculus  sandwichensis, 

3   subsp. 

Passerculus  beldingi 
Passerculus  rostratus 
Ammodramus  savannarum  austra- 
lis 

Ammodramus  s.  bimaculatus 
Passerherbulus  henslowi 
Passerherbulus  lecontei 


Passerherbulus  caudacutus 
Passerherbulus  nelsoni 
Passerherbulus  maritimus, 

2  subsp. 

Peucaea  aestivalis  botterii 
Peucaea    mexicana 
Peucaea  cassini 
Aimophila  ruficeps,  and  subsp. 
Aimophila  carpalis 
Spizella  passerina 
Spizella  p.  arizonae 
Spizella  breweri 
Spizella   pallida 
Spizella    atrogularis 
Spizella  pusilla,  and  subsp. 


WITH  WHITE  IN  NUPTIAL  PLUMAGE. 


ICTERIDAE 

Dolichonyx  orizivorus 


FAINTLY  MASKED  WITH  WHITE. 


Amphispiza  bilineata 
Amphispiza  belli 
Amphispiza  nevadensis 


191°]  Tracy:  White  Markings  in  Birds.  295 


THE  PROBLEM  DISCUSSED  FOR  BIRDS  OF  THE  OPEN. 

The  list  shows  five  families  that  carry  white  markings,  as 
against  two  families  that  do  not.  Of  the  twenty-six  species  or 
subspecies  that  carry  them,  all  but  three  are  to  be  classed  as 
flocking  birds;  and  even  these  are  unquestionably  gregarious  to 
a  marked  extent.  They  may  follow  each  other  serially  from 
place  to  place,  as  the  cactus  wren  (Heleodytes  brunneicapillus) 
and  the  sage  thrasher  (Oroscoptes  montanus),  or  they  may  flock 
for  a  limited  season,  as  the  vesper  sparrow  (Pooecetes  gram- 
ineus).  The  list  contains  the  most  perfect  types  of  flocking  birds 
in  the  whole  order,  such  as  the  meadow  pipits  of  the  genus 
Anthu8t  and  the  horned  larks  (Otocoris  alpestris),  the  lark  spar- 
rows (Chondestes  grammacus),  and  all  the  juncos.  Taken  as  a 
whole  the  white-marked  group  is  unquestionably  a  flocking  series. 
The  bearing  of  this  on  the  problem  of  white  markings  in  birds  is 
made  clear  by  a  comparison  with  the  second  list  in  which  all  but 
the  species  of  two  genera,  Leucosticte  and  Dolichonyx,  are  seen 
to  be  of  a  non-flocking,  skulking  type,  exemplified  by  the  grass- 
hopper and  Savannah  sparrows.  Of  these  two  exceptional  genera 
the  leucostictes  are  birds  of  the  Boreal  Zone  exclusively,  feeding 
on  wind-blown  insects  at  high  altitudes;  themselves  conspicuous 
through  their  dark  coloration  and,  by  virtue  of  their  Alpine- 
Arctic  habitat,  escaping  most  of  the  birds  of  prey.  In  short,  they 
are  of  an  environment  altogether  different  from  that  commonly 
referred  to  as  "open  ground"  in  the  sense  of  prairie  and  plains, 
and  may  be  eliminated  from  the  comparison.  Dolichonyx,  the 
bobolink,  on  the  other  hand,  is  a  bird  in  its  southern  habitats 
palustrine,  and  only  in  its  breeding  range  a  bird  of  the  meadows, 
where  it  displays  the  qualities  of  the  second  group,^and  is,  in 
the  case  of  the  female,  like  them  unmarked.  The  coloration 
of  the  male  in  breeding  plumage  evidently  corresponds  to  that 
of  the  marsh  blackbirds,  to  which  it  is  closely  allied.  Our  second 
listj  then,  if  it  be  found  to  contain  no  flocking  birds  but  the  two 
just  mentioned,  is  a  striking  proof  of  the  absence  of  white 
markings  in  birds  of  the  open  ground  that  do  not  flock. 

For  an  interesting  exhibition  of  correspondence  between  habit 
and  coloration,  we  turn  to  the  grasshopper  and  Sandwich  spar- 


296          University  of  California  Publications  in  Zoology.     [VOL.  6 

rows  (Ammodramus,  Passerculus) .  To  quote  a  pertinent 
description:  "Among  the  many  inconspicuous,  plain,  little 
striped-backed  sparrows  of  the  Western  United  States,  alaudinus 
is  one  of  the  commonest,  plainest,  and  most  inconspicuous 
Anywhere  in  the  meadows,  prairie  grass  or  weed  patches,  one 
may  dart  out  from  under  your  feet,  zig-zag  over  the  grass 
tops  for  a  little  way,  and  drop  into  the  grass,  hopelessly 
lost  until  he  is  again  forced  to  take  wing.  At  a  distance  you 
see  and  hear  the  birds  giving  their  plain  little  song  from  the 
top  of  a  tall  weed  or  fence  stake,  but  on  nearer  approach  they 
drop  into  the  grass  and  are  lost."  This  characteristic  is  here 
emphasized  because  in  all  of  the  species  mentioned  as  unmarked 
birds  we  shall  find  this  or  similar  traits  having  a  like  bearing 
on  our  problem,  while  in  all  of  them  the  typical  flocking  habit 
is  lacking.  The  latter  may  be  replaced  by  what  might  be  termed 
a  spurious  form  of  flocking.  As  an  instance :  the  rufous-crowned 
sparrow  (Aimophila  ruficeps),  common  on  the  Berkeley  hills, 
may  be  surprised  feeding  in  open  patches  when  it  at  once  takes 
to  brushy  cover  far  from  which  it  does  not  stray;  and  when 
traveling  moves  in  loose  bunches  of  scattered  individuals  flitting 
from  bush  to  bush  unostentatiously. 

Field  ornithologists  wall  observe,  however,  that  others  of  the 
birds  here  mentioned  are  in  some  sense  gregarious  and  gather  at 
certain  seasons  for  migratory  or  other  movements.  We  have, 
however,  evidence  to  the  effect  that  such  movements  are  some- 
times, if  not  always,  essentially  different  from  typical  flocking. 
Two  western  sparrows  from  the  arid  region  are  frequently  seen 
in  considerable  numbers  moving  from  their  southerly  winter 
range  to  a  summer  habitat  to  the  northward.  To  the  casual 
observer  they  might  appear  to  be  "flocking  birds."  A  quotation 
from  a  memorandum  made  by  Mr.  Grinnell  during  the  recent 
Museum  Expedition  to  the  region  along  the  Colorado  Biver,  will 
show  the  error  of  such  conclusions. 

"Both  Spizella  breweri  and  8.  socialis  are  now  abundant  on 
the  desert  in  migrating  flocks,  not  flocks,  however,  in  the  sense 
that  pipits  flock,  but  scattering  companies.  Each  individual  in 
a  company  moves  wholly  independently  of  any  other;  and  they 
do  not  move  en  masse  when  alarmed,  but  helter-skelter  in  different 


1910]  Tracy:  White  Markings  in  Birds.  297 

directions  around  and  through  bushes  without  call-notes.  The 
helter-skelter  disappearance  of  the  flock  certainly  puzzles  me 
and  leaves  me  wondering  where  any  one  of  the  birds  may  be 
relocated.  The  eye  gets  no  single  permanent  impression." 

The  behavior  here  cited  is  found  when  analyzed  to  be  the 
exact  opposite  of  what  occurs  in  a  typical  foraging  flock  of  birds 
having  white  rear-markings.  In  a  flock  of  pipits  the  birds  do  not 
move  independently,  as  a  rule,  in  changing  feeding  grounds; 
they  move  in  a  body  when  alarmed,  in  one  general  direction, 
with  great  uniformity;  not  through  bushes,  always  with  call- 
notes,  thus  using  every  reasonable  means  of  keeping  the  flock 
together.  Under  stress  of  alarm,  growing  darkness,  or  accidental 
scattering  through  considerable  distance,  the  bright  moving  rear- 
marks  must  at  least  be  of  appreciable  value  to  the  bird  in  keeping 
others  of  the  flock  in  sight.  Whether  or  not  that  is  the  main 
reason  for  their  existence  is,  of  course,  open  to  question. 

THE  PROBLEM  DISCUSSED  FOR  ARBOREAL  SPECIES. 

We  have  been  considering  up  to  this  point  only  the  white 
markings  characteristic  of  birds  of  the  open.  Among  arboreal 
species  the  problem  becomes  more  complicated  both  as  to 
variety  and  distribution  of  the  patterns  and  their  possible  signifi- 
cance. A  form  of  "top-white"  which  can  be  shown  to  have  the 
effect  of  making  the  wearer  conspicuous  is  the  basal  patch  of 
white  upon  flight  feathers,  usually  the  bird's  primaries.  It  need 
not  have  this  effect,  however,  when  regarded  as  a  fixed  pattern 
against  a  foliage  background.  The  latter  gives  it  a  disruptive 
value,  as  Thayer  (1909)  has  shown  for  similar  designs.  In  order 
to  test  the  concealing  values  of  this  particular  wing  marking  I 
mounted  the  green-backed  goldfinch  (Astragalinus  psaltria 
hesperophilus)  and  the  black-headed  grosbeak  (Zamelodia  melan- 
ocephala)  with  spread  wings  and  photographed  them  against 
sunlit  foliage  and  backgrounds  of  leaves  with  spaces  of  sky 
showing  through  them.  The  birds  were  difficult  to  find  in  the 
resulting  prints.  Undoubtedly  the  photographs  by  their  lack 
of  relief  exaggerated  the  concealing  effect ;  yet  that  there  is  such 
an  effect,  in  general,  it  is  safe  to  admit. 


298          University  of  California  Publications  in  Zoology.     [VOL.  6 

When,  however,  the  bird  takes  wing  a  wholly  different  prin- 
ciple comes  into  play.  Suppose  it  be  the  goldfinch  that  has  left 
its  perch.  What  we  actually  see  is  a  pair  of  wings  opened  and 
closed,  alternately  revealing  and  concealing  a  pattern  which  finds 
no  background  to  blend  with,  because  it  consists  of  intermittent 
flashes  of  white,  not  haphazard  like  the  ruffling  of  leaves,  but 
rhythmical,  emphasizing  the  essential  features  of  the  flying  bird. 
This  is  not  speculation  but  a  description  of  facts — it  is  what  one 
sees  in  the  field.  Those  wTho  are  unfamiliar  with  the  bird  named 
may  recall  a  similar  flight-effect  in  the  black-throated  blue 
warbler  (Dendroica  caerulescens) ,  and  even  more  striking  pat- 
terns in  the  common  shrike  (Lanius  ludovicianus).,  the  mocking- 
bird (Mimus  polyglottos)  and  the  "black  mocker"  (Phainopepla 
nit  ens).  Concealed  wing  patterns  are  not  the  only  ones  that 
become  conspicuous  in  flight.  Obviously  any  white  pattern 
located  on  primaries,  secondaries,  tertials,  or  wing  coverts,  will 
be  expanded  to  the  greatest  extent  during  the  motions  of  flight. 
It  happens  that  even  the  comparatively  obscure  wing  bars  of  the 
lazuli  bunting  (Passerina  amoena)  are  easily  distinguished  as 
white  bands  on  the  flying  bird.  The  white  of  scapular  feathers, 
as  in  the  magpie,  is  emphasized  in  the  same  way.  Tail  blotches 
on  some  warblers  reveal  their  whereabouts  as  they  flit  from  twig 
to  twig,  rather  than  conceal  them.  I  have  not,  therefore, 
attempted  to  distinguish  various  classes  of  top  markings  among 
arboreal  birds  with  a  view  to  finding  special  functions  for  each. 
It  is  precisely  such  attempts  that  have  discredited  theories  of 
the  functions  of  these  markings.  Arbitrary  distinctions  do  not 
occur  in  nature. 

In  order  to  give  the  reader  an  opportunity  to  review  the 
entire  series  of  white-patterned  birds  and  to  compare  it  with  the 
complete  series  of  those  that  lack  top-white,  I  have  prepared  the 
accompanying  lists.  One  family,  the  Mniotiltidae,  has  been 
reserved  for  more  detailed  study,  and  is  given  in  a  separate  list. 
The  ground-frequenting  birds  of  the  open  have  already  been 
given.  These  lists,  therefore,  are  fully  representative  of  arboreal 
perching  birds  of  the  temperate  zone,  and  include  all  species 
of  the  order  Passeriformes  regularly  found  in  the  United  States. 


1910] 


Tracy:  White  Markings  in  Birds. 


299 


PASSERIFORM  BIRDS  OF  ARBOREAL   HABIT. 
A.      BIRDS   WITH   WHITE    WING   OR   TAIL    MARKINGS. 


FRINGILLIDAE 

Hesperiphona  vespertina 

Pinicola  enudeator  leucura 

Loxia  leucoptera 

Astragalinus  tristis 

Astragalinus  psaltria 

Astragalinus    psaltria    hespero- 
philus 

Zamelodia  melanocephala 

Zamelodia    ludoviciana 

Passerina  amoena 

Sporophila  morelleti  sharpei 

Spizella  monticola 

Pipilo   erythrophthalmus 

Pipilo   maculatus 
LANIIDAE 

Lanius  borealis 

Lanius  ludovicianus 

VlREONIDAE 

Lanivireo  solitarius 
Vireo   'belli 
Vireo  huttoni 

ICTERIDAE 

Icterus  nelsoni 

Icterus     melanocephalus     audu- 

boni 

Icterus  cucullatus  sennetti 
Icterus  bullocki 
Icterus  parisorum 
Xanthocephalus   xanthocephalus 
TROGLODYTIDAE 

Mimus  polyglottos 


TURDIDAE 

Myadestes  townsendi 
Planesticus    migratorius 
Planesticus  confinis 

SlTTIDAE 

Sitta   canadensis 
Sitta  pygmaea 

CORVIDAE 

Nucifraga  columbiana 
Pica  pica  hudsonia 
Pica  nuttalli 
Cyanocitta  cristata 

TYRANNIDAE 

Muscivora  forficata 
Tyrannus  tyrannus 
Tyrannus  verticalis 
Myiarchus  cinerascens 
Myiarchus  ma  gist  er 
Sayornis  nigricans 

SYLVIIDAE 

Polioptila  caerulea 
Polioptila  californica 
Polioptila  plumbea 

HlRUNDINIDAE 

Hirundo  erythrogaster 
Tachycineta  thalassina 

BOMBYCILLIDAE 

Bombycilla  garrula 
Phainopepla  nitens 
PARIDAE 

Penfhestes  atricapillus 


B.      BIRDS   WITHOUT   WHITE    WING   OR   TAIL   MARKINGS. 


TURDIDAE 

Ixoreus  naevius 
Hylocichla  mustelina 
Hylocichla  fuscescens 
HylocicTila  guttata 
Hylocichla  ustulata 
Hylocichla  aliciae 
Sialia  sialis 
Sialia   mexicana 


Sialia  currucoides 
Cyanosylvia  suecica  robusta 

CINCLIDAE 

Cinclus    mexicanus   unicolor 

SYLVIIDAE 

Acanthopneuste  borealis 
Eegulus   calendula 
Eegulus  satrapa 


300         University  of  California  Publications  in  Zoology.     tv°L-  6 


CHAMAEIDAE 

Chamaea  fasciata 

PARIDAE 

Baeolophus  bicolor 
Baeolophus  inornatus 
Baeolophus  atricristatus 
Baeolophus  wollweberi 
Penthestes  atricapillus 
Penthestes  carolinensis 
Penthestes  sclateri 
Penthestes  gambeli 
Penthestes  rufescens 
Penthestes  hudsonicus 
Penthestes  cinctus  alascensis 
Psaltriparus  minimus 
Psaltriparus  melanotis  lloydi 
Auriparus  flaviceps 

SlTTIDAE 

Sitta  carolinensis 

CERTHIIDAE 

Certhia  familiaris 

TROGLODYTIDAE 

Dumetella   carolinensis 
Toxostoma  bendirei 
Toxostoma  redivivum 
Toxostoma  lecontei 
Toxostoma  crissale 
Toxostoma  cinereum 
Toxostoma  longirostre 
Toxostoma  rufum 
Toxostoma  curvirostre 
Salpinctes  obsoletus 
Salpinctes  guadalupensis 
Catherpes  mexicanus 
Thryothorus  ludovicianus 
Spiza  americana 
Arremonops  rufivirgata 
Guiraca    caerulea 
Passerina  cyanea 
Passerina  versicolor 
Passerina  ciris 
Pyrrhuloxia  sinuata 
Pipilo  fuscus 
Pipilo  crissalis  senicula 
Oreospiza  chlorura 

TANGARIDAE 

Piranga  ludoviciana 


Piranga  erythromelas 
Piranga  hepatica 
Piranga  rubra 

ICTERIDAE 

Molothrus  ater 

Tangavius  aeneus  involucratus 

Agelaius  phoeniceus 

Agelaius  gubernator  calif  ornicus 

Agelaius   tricolor 

Euphagus   carolinus 

Quiscalus   quiscula 

Quiscalus   major   macrourus 

CORVIDAE 

Cyanocitta  stelleri 

Aphelocoma  -woodhousei 

Aphelocoma  cyanotis 

Aphelocoma  calif omica 

Aphelocoma  texana 

Aphelocoma  sieberi 

Aphelocoma  insularis 

Xanthoura  luxuosa  glaucescens 

Perisoreus  canadensis 

Perisoreus    obscurus 

Corvus  corax 

Corvus  cryptoleucus 

Corvus  brachyrhynchos 
TYRANNIDAE 

Tyrannus   melancholicus   couchi 

Tyrannus  vociferans 

Pitangus  sulphuratus  derbianus 

Myiodynastes  luteiventris 

Myiarchus  crinitus 

Myiarchus   lawrencei   olivascens 

Sayornis  phoebe 

Sayornis  saya 

Nuttallornis   borealis 

Myiochanes  pertinax  pallidiven- 
tris 

Myiochanes  virens 

Myiochanes  richardsoni 

Thryomanes   bewicJci 

Thryomanes  leucophrys 

Thryomanes    brevicauda 

Troglodytes  aedon 

Troglodytes  parkmani 

Nannus  hiemalis 

Telmatodytes  palustris 

Cistothorus  stellaris 


1910] 


Tracy:  White  Markings  in  Birds. 


301 


FBINGILLIDAE 

Pyrrhula  cassini 
Carpodacus  purpureus 
Carpodacus  cassini 
Carpodacus  mexicanus  frontalis, 

and  other  subsp. 
Carpodacus  amplus 
Loxia    curvirostra 
Acanthis    linaria 
Acanthis  hornemanni 
Spinus  pinus 
Astragalinus  lawrencei 
Cardinalis  cardinalis 
Melospiza  melodia 
Melospiza  georgiana 
Melospiza  lincolni 
Zonotrichia  albicollis 
Zonotrichia  leucophrys 
Zonotrichia    coronata 
Zonotrichia  querula 
Passerella  iliaca 
Empidonax    difficilis 
Empidonax    flaviventris 
Empidonax  trailli 
Empidonax  minimus 


Empidonax  hammondi 
Empidonax  wrighti 
Empidonax  virescens 
Empidonax  griseus 
Empidonax  fulvifrons 
Pyrocephalus     rubineus 
canus 

Camptostoma  imberbe 

HlRUNDINIDAE 

Progne   chalybea 
Progne  subis 
Progne  cryptoleuca 
Iridoprocne    bicolor 
Riparia  riparia 

BOMBYCILLIDAE 

Bombycilla  cedrorum 

VlEEONIDAE 

Vireosylva  olivacea 
Vireosylva  philadelphica 
Vireosylva   gilva 
Lanivireo   flavifrons 
Vireo  atricapillus 
Vireo  griseus 
Vireo  vicinior 


mexi- 


The  facts  as  to  the  distribution  of  white  markings  among 
birds  of  the  various  local  associations  may  be  gathered  from  a 
study  of  the  first  list.  It  also  affords  a  basis  for  finding  any 
agreement  of  physical  or  temperamental  characters  among  birds 
so  marked,  or  the  occurrence  of  habits  that  may  have  a  bearing  on 
their  coloration.  A  similar  purpose  is  served  by  the  second  list 
—with  this  drawback :  it  includes  a  number  of  color  features  that 
may  be  of  a  value  similar  to  that  of  white  patterns,  and  even 
more  revealing.  Accordingly  we  need  not  be  surprised  if  we 
find  among  species  bearing  such  features,  for  example,  nearly  all 
the  crows  and  blackbirds,  the  habits"  and  distribution  that 
are  characteristic  of  white-marked  birds. 

There  is,  moreover,  a  correspondence,  especially  among  the 
unmarked  groups,  that  appears  to  be  due  primarily  to  intrinsic 
influences  producing  family  characters;  like  all  color  characters 
these  are  too  inconstant  for  the  systematist  to  utilize.  Still,  in 
some  cases  they  suggest  a  persistence  of  some  ancestral  type 
dominating  extrinsic  influences.  Such  a  correspondence  is  seen 


302          University  of  California  Publications  in  Zoology.     [VOL.  6 

in  the  family  of  wrens  which  an  amateur  can  usually  recognize 
by  noting  the  superficial  color  pattern.  A  similar  tendency 
appears  in  the  vireos  and  also  in  the  flycatchers.  If,  therefore, 
we  find  white  patterns  conspicuously  lacking  among  Troglo- 
dytidae,  Vireonidae  and  Tyrannidae,  we  are  bound  to  consider 
whether  or  not  this  may  be  partly  due  to  the  stability  of  a  type 
(intrinsic  influence)  or  to  selective  influences  alone.  The  occur- 
rence of  a  perfect  adaptation  at  variance  with  the  type  in  the 
bleached,  sand-colored  monochrome  of  the  Leconte  thrasher 
(Toxostoma  lecontei)  indicates  that  the  Troglodytidae  may  not 
be  exempt  from  the  strict  enforcement  of  the  principles  of 
adaptive  coloration,  where  the  conditions  of  their  life  demand  it. 

There  are  some  relative  differences  among  birds  that  might 
conceivably  enter  into  the  explanation  of  correspondences  in 
color,  but  apparently  do  not  to  an  appreciable  extent.  Size  is  one 
of  these.  The  only  way  in  which  it  appears  to  affect  coloration 
is  by  affording  immunity  from  enemies.  Size  combined  with 
vigor  and  aggressiveness  opens  the  way  for  conspicuous  colora- 
tion. But  the  need  of  concealment  on  the  part  of  the  aggressor 
neutralizes  the  effect  of  this  immunity  in  most  cases.  The  raven 
is  one  of  the  exceptions  within  the  order  of  perchers,  and  the 
condor,  Egyptian  vulture,  and  turkey  buzzard,  outside  it.  These 
are  birds  that  need  no  concealment  for  aggression,  but  profit  by 
a  conspicuousness  that  makes  them  recognizable  to  each  other  at 
great  distances. 

As  for  warning  coloration,  there  seems  no  reason  for  believing 
that  it  occurs  among  perching  birds.  Were  the  principle  thor- 
oughly established  we  might  be  justified  in  regarding  the  magpie 
as  an  instance ;  but  since  other  functions  may  readily  be  assigned 
to  the  contrasts  in  its  plumage,  and  since  these  are  not  necessarily 
utilitarian,  as  the  bird  is  largely  ' '  immune, ' '  the  whole  hypothesis 
is  negligible  for  the  birds  under  discussion. 

Temperamental  differences  form  another  set  of  elements  to  be 
considered.  A  search  for  correspondences  in  this  direction  shows 
at  least  a  few  well  attested  instances  of  boldness  of  disposition 
accompanying  the  supposed  conspicuousness  of  plumage.  Such 
are  the  kingbird  (Tyrannus  tyrannus),  the  scissor-tailed 
flycatcher  (Muscivora  forficata),  the  mockingbird  (Mimus  poly- 


191°]  Tracy:  White  Markings  in  Birds.  303 

glottos),  the  magpie  (Pica  hudsonia),  and  the  shrike  (Lanius 
borealis).  These  are  interesting  cases,  but  little  can  be  inferred 
from  them  as  to  the  significance  of  white  markings  in  the  group 
at  large. 

It  is  in  the  correlation  of  special  color  features  with  special 
feeding  and  breeding  ranges  that  we  get  the  first  clear  indication 
of  a  large  underlying  principle  determining  which  birds  shall 
possess  the  white  pattern  and  which  shall  not.  The  top-marked 
finches  are  seen  to  be  birds  of  open  woods  mainly,  largely  of 
roving  disposition  and  wide  feeding  range.  Unmarked  species 
of  the  family  are  mainly  birds  of  low  zones  and  narrower  feeding 
beat.  Only  two  of  the  first  list  are  characteristically  low  rangers 
and  given  to  covert-seeking:  these  are  our  eastern  and  western 
white-marked  towhees  (Pipilo  erythrophthalmus  and  P.  macu- 
latus).  On  the  other  hand  nearly  all  of  the  second  list  are  either 
confined  to  close  foliage  of  medium  height,  or  belong  to  such 
associations  as  the  rank  growth  of  humid  regions,  the  dark 
borders  of  shady  swamps,  or  thickets  of  the  chaparral  belt.  They 
are  the  thrushes,  painted  in  monochrome  above ;  warblers, 
lacking  top-patterns ;  wrens  with  their  finely  barred  color 
scheme ;  flycatchers  with  dull  olivaceous  or  other  uniform  shad- 
ings.  These  are  correspondences  that  surely  have  significance, 
and  require  for  their  interpretation  something  more  than  the 
older  theories  of  coloration  could  offer. 

Finding  such  good  illustrations  of  the  disruptive  effect  of 
white  or  bright  patterns  among  animals  and  birds,  the  authors 
of  "Concealing  Coloration  in  the  Animal  Kingdom"  (Gerald 
and  A.  H.  Thayer,  1909),  have  come  to  believe  that  no  other 
explanation  is  needed  to  account  for  the  presence  of  top-white  in 
birds  that  show  themselves  against  the  sky,  than  natural  selection 
working  through  this  means.  Their  belief  accords  with  the 
conditions  just  cited.  It  does  not,  however,  take  account  of  the 
fact  already  mentioned  that  markings  often  become  conspicuous 
during  the  flight  of  the  bird,  nor  does  it  take  note  of  the  corre- 
lation that  has  been  shown  to  exist  among  open-ground  birds, 
of  flight-revealed  markings  with  the  flocking  habit — a  condition 
which  we  shall  also  find  largely  present  among  the  arboreal  birds. 
In  the  use  of  these  lists  of  birds  to  determine  the  latter  point, 


304         University  of  California  Publications  in  Zoology.     tv°L-  6 

the  very  arbitrariness  of  the  grouping  tends  to  be  misleading. 
A  list  of  all  perching  birds  that  have  color  features  tending  to 
conspicuousness  in  flight  (whether  white  or  some  other  color), 
would  correspond  much  more  nearly  to  a  complete  list  of  the 
flocking  birds.  It  would  include  the  gregarious  species  of  the 
family  Icteridae  which  mainly  lack  white  patterns.  It  would 
include  the  pine  siskin  (Spinus  pinus)  which  has  yellow  wing 
markings  instead  of  white.  Yet,  even  as  it  stands,  the  list  is  very 
suggestive.  When  we  consider  the  value  to  all  birds  ranging  in 
the  open  foliage  of  instant  recognition  at  a  distance,  and  sight- 
clues  for  the  purpose  of  keeping  together,  wre  shall  not  easily 
believe  that  wing  and  tail  white  are  solely  features  of  concealing 
coloration.  Their  revealing  function  during  flight  is  entirely  in 
harmony  writh  their  concealing  functions  when  at  rest. 

An  apt  illustration  of  this  harmony  of  functions  is  found  in 
the  following  description  of  the  western  evening  grosbeak 
(Bailey,  1902,  p.  308)  : 

"On  a  Sierra  grade  we  have  passed  a  flock  busily  gathering 
wild  cherries  in  a  bush  beside  the  road,  and  when  camped  under 
the  firs  of  Mt.  Shasta  have  had  wandering  bands  stop  for  a  drink 
from  the  camp  brook,  delighting  us  by  their  striking  yellow 
and  wrhite  plumage.  Although  they  are  so  highly  colored  and 
in  flight  their  white  wing  patches  make  such  prominent  directive 
marks,  this  very  yellow  and  white  coloration  often  becomes  posi- 
tively protective.  While  watching  the  birds  on  Mt.  Shasta  one 
day,  I  was  struck  by  the  conspicuousness  of  one  that  flew  across 
an  open  space.  As  it  lit  on  a  dead  stub  whose  silvery  branches 
were  touched  with  yellow  lichen,  to  my  amazement  it  simply  van- 
ished. Its  peculiar  greenish  yellow  toned  in  perfectly  with  the 
greenish  yellow  of  the  lichen. " 

It  is  of  interest  to  note  that  the  above  observation  was  made 
before  the  disruptive  effect  of  white  patterns  had  been  demon- 
strated by  Thayer  (1909),  or  the  theory  of  their  directive 
function  seriously  questioned.  There  could  be  no  better 
instance  than  the  one  cited,  of  a  double  office  performed  by  a 
single  color  feature — revealing  in  flight,  concealing  when  in 
repose.  Precisely  this  relation,  I  believe,  exists  through  the 
group  as  a  whole 


1910] 


Tracy:  White  Markings  in  Birds. 


305 


SPECIAL  STUDY  OF  THE  MNIOTILTIDAE 

For  a  more  minute  study  of  the  relation  of  white  color  marks 
to  a  bird's  habitual  range  I  have  chosen  the  American  wood 
warblers.  Not  only  are  the  members  of  this  family  very  well 
distributed  among  the  more  or  less  well  defined  strata  of  local 
vegetation,  but,  unlike  the  Sylviidae  or  old  world  warblers,  they 
show  the  highest  degree  of  specialization  both  in  regard  to  variety 
of  pigments  and  to  white  patterns.  It  seemed  worth  while, 
therefore,  to  investigate  the  actual  distribution  of  the  species  in 
the  three  categories  of  high  or  open  foliage,  medium,  and  low 
or  close  coverts.  The  results  of  such  a  study  are  embodied  in 
the  following  table  in  which  the  mean  height  of  the  bird's 
occurrence  has  been  compared  with  that  of  its  average  nesting 
site  as  recorded  by  numerous  observers,  and  its  feeding  beat 
gauged  with  some  accuracy.  While  it  has  not  always  been 
possible  to  distinguish  clear  lines  of  demarkation,  on  the  whole 
there  is  a  surprising  agreement  among  writers  who  allude  to 
the  feeding  levels  of  the  warblers. 

WAEBLEES  WITH  WHITE  WING  OB  TAIL  MASKING  S. 


OF  HIGHEST  EANGE. 


Vermivora  bachmani 
Compsothlypis  americana 
Compsothlypis  a.  usneae 
Compsothlypis  pitiayumi 

nigrilora 

Peucedramus  olivaceus 
Dendroica    magnolia 
Dendroica  tigrina 
Dendroica  auduboni 
Dendroica  nigrescens 
Dendroica  virens 


Mniotilta   varia 
Protonotaria  citrea 
Vermivora  chrysoptera 
Vermivora  pinus 
Dendroica  coronata 


Dendroica  caerulescens 
Dendroica  pensylvanica 


Level  of  Nest. 

r-3' 

8'  + 
8'  + 

8'  + 
30'-50' 
3'  + 
3'  + 
4'-50' 
5'-52' 
3'-40' 


Dendroica  chrysoparia 
Dendroica    occidentalis 
Dendroica  caerulea 
Dendroica  fusca 

(Syn.  blackburniae) 
Dendroica  dominica 
Dendroica  graciae 
Dendroica  castanea 
Dendroica  striata 
Dendroica  vigor  si 


OF  INTERMEDIATE  EANGE. 

ground  Dendroica  Icirtlandi 

5'-25'  Dendroica  discolor 

ground  Wilsonia  citrina 

ground  Cardellina  rubrifrons 

4'-20'  Setophaga  picta 

OF  LOWEST  EANGE. 

l'-3'  Dendroica  palmarum 

2'   av 


Level  of  Nest. 

15' av. 

2'-45' 

40'-70' 

20'-84' 

20'-90' 

50'-60' 

15'-20' 

l'-10' 

8'-80' 


ground 

ground 
ground 

ground 


306          University  of  California  Publications  in  Zoology.     tv°L-  6 


WARBLEKS   WITHOUT   WHITE    MARKINGS. 
OF  INTERMEDIATE  RANGE. 

Level  of  Nest.  Level  of  Nest. 

Vermivora  peregrina  ground  Oporornis  tolmiei  6"-4' 

Vermivora  celata  celata  ground  Wilsonia   pusilla   chryseola  3'-5' 

Vermivora  c.  lutescens  ground  Wilsonia  canadensis  ground 

Vermivora  c.  sordida  2'-8'  Setophaga   ruticilla  2'-30' 

Vermivora  rubricapilla  ground  Dendroica  aestiva  3'-25' 

Oporornis   Philadelphia  6'-20' 

OF  LOWEST  RANGE. 

Helinaia  swainsoni  ground  Oporornis  formosa  ground 

Helmitheros  vermivorus  ground  Oporornis  agilis  ground 

Vermivora  virginiae  ground  Geothlypis  trichasr  ground 

Vermivora  luciae  2'-6'  Geothlypis   t.    occidentalis  6"-5' 

Seiurus  aurocapillus  ground  Icteria  virens  l'-5' 

Seiurus   motacilla  ground  Wilsonia  pusilla  ground 

Seiurus  novel) or acensis  ground 

Of  the  fifty-seven  warblers  here  treated,  thirty-three  have 
well-defined  white  top-patterns.  Of  these,  twenty  are  high 
rangers,  a  number  of  them  emphasizing  their  preference  by 
choosing  a  nesting  site  at  the  extraordinary  level  of  seventy, 
eighty,  or  even  ninety  feet  from  the  ground. 

It  is  a  curious  fact  that  a  careful  sifting  of  the  recorded 
observations  discovers  no  unmarked  warbler  belonging  properly 
to  the  high  feeding  beats.  A  few,  such  as  Vermivora  celata,  occur 
at  variable  heights  and  may  be  seen  in  the  tops  of  trees ;  but  these 
usually  nest  low,  upon  or  near  the  ground,  and  are  usually 
assigned  an  intermediate  feeding  beat.  It  seems  to  be  true  on 
the  whole  that  the  plain  "protectively  colored"  warblers  are 
unrepresented  in  the  upper  strata  of  our  deciduous  forests,  that 
they  are  common  at  the  medium  levels,  and,  as  shown  in  the  table, 
belong  mainly  in  the  lower  stratum,  that  of  thickets,  brush 
areas,  tangles  about  marshy  places.  Briefly  put,  the  situation 
among  warblers  seems  to  be:  no  plain  plumages  seen  at  the 
highest  levels.  But  the  converse — no  marked  plumages  at  lowest 
levels — is  not  strictly  true.  No  arbitrary  line  is  drawn.  About 
the  same  number  of  the  marked  and  unmarked  occupy  the  inter- 
mediate feeding  beats  and  nesting  sites.  It  seems  reasonable  to 
infer,  however,  from  the  results  shown  by  this  tabulation  that 


191°]  Tracy:  White  Markings  in  Birds.  307 

top-patterns  have  decided  utilitarian  value  to  high-ranging 
warblers.  That  the  value  of  white  patterns  is  at  a  minimum  for 
ground  nesters  and  low  feeders,  seems  to  be  as  clearly  demon- 
strated. 

For  those  who  find  the  arguments  for  the  concealing  functions 
of  top-white  conclusive,  the  table  will  primarily  serve  as  evidence 
of  the  correctness  of  Mr.  Thayer  's  interpretation.  And  such  they 
are  in  so  far  as  they  corroborate  the  view  that  birds  often  seen 
against  open  foliage  with  sky-illuminated  spaces  should  have  and 
do  have  bright  patches  imitating  these  spaces.  There  may  be 
no  opposing  view  that  can  rob  this  one  of  its  convincing  power 
once  it  has  been  perceived.  There  is,  however,  a  further  con- 
sideration deserving  attention. 

High  and  open  foliages  involve  more  than  a  broken  sky 
and  leaf  background  with  the  need  for  imitating  them.  They 
involve  wider  spaces  to  travel;  the  ability  to  see  companions  at 
a  greater  distance;  the  need  of  seeing  and  keeping  track  of 
them  by  other  means  than  call-notes;  the  long  continued  habit 
of  so  doing. 

The  warblers  are  among  the  most  mutually  dependent  of 
birds,  the  least  solitary,  migrating  in  flocks  and  social  during  the 
daytime-portions  of  their  travel.  Among  the  least  social  the 
shyest  and  most  retiring  of  the  family  are  the  plain  or  somber- 
hued  species,  including  the  so-called  water  thrushes  (Seiurus 
noveboracensis  and  8.  motacilla)  and  the  Connecticut  and  mourn- 
ing warblers  (Oporornis  agilis  and  0.  Philadelphia).  The  bolder, 
the  most  familiar,  are  in  the  Dendroica  group  (Dendroica 
coronata,  maculosa,  auduboni,  etc.).  This  need  not  be  a  mere 
coincidence.  We  have  noticed  the  same  tendency  in  the  order  at 
large.  With  a  preference  for  close,  leafy  coverts  and  secluded 
forest  ways  go  the  somberer  tones,  the  monochrome  coloration, 
and  shy,  furtive  habits.  With  a  preference  for  open  woods  and 
roving  ways,  greater  distances  and  separations  to  be  adjusted, 
have  come  the  greatest  variety  of  top-patterns  among  birds, 
many  of  them  showing  excellent  devices  for  a  revealing  flight 
from  the  opening  wing. 


308         University  of  California  Publications  in  Zoology.     tv°L-  6 

SEXUAL    SELECTION    AS    AFFECTING    WHITE    PAT- 
TERNS. 

It  remains  for  us  to  touch  on  the  question,  does  sexual  selec- 
tion enter  into  the  problem  of  white  patterns?  For  open- ground 
birds  we  can  promptly  answer  that  it  does  not.  There  are,  how- 
ever, many  instances  among  arboreal  birds  where  the  white 
marking  is  intensified  in  the  male.  This  very  fact  militates 
against  the  physiological  contention  that  greater  vigor  in  the 
male  sex  accounts  for  all  color  differences.  White  blotches  or 
bars  are  caused  by  the  absence  of  pigment.  Were  it  not  for 
the  more  intense  coloration  of  other  parts  we  might  conclude 
on  this  basis  that  the  white-marked  male  is  deficient  in  vigor. 
It  also  argues  against  the  view  that  white  patches  afford  the 
best  possible  concealing  pattern,  for  in  that  case  the  female 
should  not  have  them  obscured.  Adherents  of  the  directive 
theory  may  find  support  for  their  views  in  the  fact  that  white 
wing  bars  do  actually  persist  in  the  female  in  many  cases,  as 
in  the  pine  grosbeak  (Pinicola  enucleaior)  and  the  white- 
winged  crossbill  (Loxia  leocoptera)  and  others,  so  that  it  cannot 
be  regarded  as  due  solely  to  sexual  selection.  The  analogy  in 
the  case  of  open-ground  birds  where  both  sexes  are  alike,  as  a 
rule,  strengthens  the  directive  interpretation.  Further,  if  we 
are  right  in  assuming  that  the  male  is  the  more  vigorous  and 
the  leader  of  bird  movements,  then  there  is  ground  for  believing 
that  white  markings,  even  though  intensified  in  the  male,  are 
directive  in  some  sense.  That  such  a  relation  exists  among 
warblers  was  the  belief  of  Dr.  Coues  when  he  wrote  the  following 
paragraph  descriptive  of  the  warbler  family : 

"Some  travel  true  to  the  meridian  in  hours  of  darkness, 
stopping  at  daybreak  from  their  lofty  flights  to  rest  and  recruit 
for  the  next  stage  of  the  journey.  Others  pass  more  leisurely 
from  tree  to  tree  in  a  ceaseless  tide  of  migration,  gleaning  as  they 
go.  The  hardier  males  in  full  song  and  plumage  lead  the  way 
for  the  weaker  females  and  yearlings. ' ' 


Tracy:   White  Markings  in  Birds.  309 

DIRECTIVE  MARKINGS  OUTSIDE  THE  ORDER 
PASSERIFORMES. 

An  instance  of  revealing  coloration  outside  the  order  Passer- 
iformes  seems  worth  citing  since  the  very  existence  of  a  principle 
of  directive  coloration  has  been  questioned  (Thayer,  1900).  The 
wings  of  the  nighthawks,  both  eastern  and  western  species,  are, 
as  is  well  known,  marked  with  a  single  white  spot  in  each. 
Far  from  tending  to  merge  the  bird's  contour  with  anything  in 
the  background,  these  spots  easily  reveal  and  characterize  the 
bird  to  observers.  Even  were  there  need  for  the  nighthawks  in 
their  swift,  crepuscular  flights  to  be  hidden  from  winged  pur- 
suers, it  is  hardly  credible  that  the  spots  should  serve  this 
purpose.  The  Texas  nighthawk  (Chordeiles  acutipennis  tex- 
ensis}  is  known  to  have  a  habit  which  gives  revealing  effect  to 
the  white  throat-patch,  as  well  as  that  on  the  wing.  This  throat 
patch  is  concealed  as  the  bird  takes  its  daytime  rest  in  the 
open;  but  when  surprised  upon  its  nest  it  adopts  the  familiar 
wounded  bird  tactics  to  divert  attention.  After  fluttering  a 
short  distance  it  faces  the  intruder,  elevates  and  depresses  its 
breast,  thus  appearing  to  make  every  effort  to  hold  the  attention 
of  its  enemy.  Such  a  motion  adds  decidedly  to  the  conspicuous- 
ness  of  the  white  patch.  This  effect  of  a  pattern  and  correspond- 
ing behavior  of  the  bird  is  perhaps  unique,  but  it  seems  at  least 
to  establish  a  case  of  the  revealing  function  of  white. 

CONCLUSION. 

This  paper  has  attempted  to  test  the  validity  of  the  older 
interpretation  of  white  markings  in  birds  by  analyzing  their 
mode  of  occurrence  in  a  single  order,  and  to  harmonize  it,  if 
valid,  with  a  newer  and  apparently  contradictory  interpretation. 
It  has  shown  that  there  is  good  ground  for  believing  that  flight- 
exposed  markings,  whatever  their  mode  of  evolution,  are  of 
actual  utility  to  birds  as  sight-clues,  whether  occurring  in  the 
comparatively  uniform  rear  markings  of  the  open  ground  species, 
or  the  varied  top  patterns  of  the  arboreal.  It  has  called  atten- 
tion to  a  decided  correlation  of  the  markings  with  the  habit  of 


310         University  of  California  Publications  in  Zoology.     IToL-  6 

flocking,  as  well  as  with  that  of  open  ranging.  It  has  shown 
that  sexual  selection  can  only  have  operated  in  producing  a  more 
sharply  defined  pattern  in  the  male,  but  cannot  account  for  the 
existence  of  the  pattern  itself.  Recent  views  as  exemplified  in 
Thayer  (1909)  as  to  the  concealing  effect  of  white  markings 
have  been  regarded  as  greatly  simplifying  the  problem  and 
aiding  our  understanding  of  the  possible  meaning  of  the  patterns. 
This  newer  view,  however,  is  found  to  be  in  perfect  accord  with 
the  older  one  known  as  the  Theory  of  Directive  Markings.  It 
restricts  the  application  of  the  latter,  however,  to  patterns  that 
can  be  shown  to  be  conspicuous. 

These  considerations  cannot  be  regarded  as  affording  evidence 
in  an  ultimate  sense.  They  lead  at  best  to  the  provisional 
modification  of  an  interpretation  that  was  open  to  criticism,  and 
tend  to  check  over-emphasis  upon  the  concealing  principle  in 
animal  coloration.  Doubtless  they  fall  short  of  reaching  the  full 
meaning  of  the  white  or  bright  patterns  of  passeriform  birds. 
Possibly  the  interpretation  of  diverse  coloration  as  having  de- 
veloped under  conditions  of  comparative  immunity,  from  such 
sources  of  attack  as  those  to  which  terrestrial  animals  are  subject 
needs  greater  emphasis  than  has  been  given  it. 


191°]  Tracy:  White  Markings  in  Birds.  311 


LITERATURE  CITED. 


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Chapman,  F.  M. 

1907.  The  warblers  of  North  America.  New  York,  1907;  8vo.,  pp. 
i-viii,  1-306,  24  pis.,  12  half-tone  pis. 

Coues,  E. 

1903.  Key  to  North  American  Birds.    Boston,  1903 ;  roy.  8vo.,  pp.  i-xli, 

1-1152,  v.  1  and  2,  3  pis.,  747  text  figures. 

Cunningham,    J. 

1900.  Sexual  dimorphism  in  the  animal  kingdom.  London,  1900;  8vo., 
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Jones,  L. 

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Thayer,  A.  H. 

1900.  Arguments  against  the  banner-mark  theory.  Auk,  v.  17,  pp.  108- 
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map,  37  text  figures. 


Vol.  3.     1.  Some   Observations   on  the  Nervous  System  of  Copepoda,  by   0.  6. 

Esterly.     Pp.  1-12,  plates  1-2.     January,  1906 .25 

2.  (IX)*    Ostracoda  of  the    San    Diego    Region.     1.  Halocypridae,  by 

Chancey  Juday.    pp.  13-38,  plates  3-7.     April,  1908 30 

3.  (X)    The  California  Shore  Anemone,   Bunodactis  xanthogrammica,  by 

Harry  Beal  Torrey.     Pp.  41-48,  plate  8,  April,  1906. 

4.  (XI)  Sexual  Dimorphism  in  Aglaophenia,  by  Harry  Beal  Torrey  and 

Ann  Martin.     Pp.  47-52,  9  text-figures.    April,  1906. 

Nos.  3  and  4  in  one  cover 15 

5.  (XII)  New  Copepod  Fauna  from  the  San  Diego  Region,  by  Calvin  Olin 

Esterly.     Pp.  53-92,  plates  9-14,    December,  1903 35 

6.  (XII)  DinoHagellata  of  the  San  Diego  Region,  II.     On  Triposolenia,  a 

New  Genus  of  the  Dinophysidae,  by  Charles  Atwood  Kofoid.  Pp. 
93-116,  plates  15-17. 

7.  A  Discussion  of  the  Species  Characters  in  Triposolenia.    I.  The  Nature 

of  Species  Characters.  II.  The  Adaptive  Significance  of  Species 
Characters.  III.  The  Coincident  Distribution  of  Related  Species. 
By  Charles  Atwood  Kofoid.  Pp.  117-126. 

8.  On  the  Significance  of  the  Asymmetry  in  Triposolenia,  by  Charles 

Atwood  Kofoid.     Pp.  127-133. 

Nos.  6,  7,  and  8  in  one  cover.    December,  1906 36 

9.  (XIV)   Ostracoda  of  the  San  Diego  Region.    II.  Littoral  Forms,  by 

Chancey  Juday.    Pp.  135-156,  plates  18-20. 

10.  (XV)   Cladocera  of  the  San  Diego  Region,  by  Chancey  Juday.    Pp. 

157-158,  1  text  figure. 

Nos.  9  and  10  in  one  cover.    January,  1907... 25 

11.  (XVI)  The  Marine  Fishes  of  Southern  California,  by  Edwin  Chapin 

Starks  and  Earl  Leonard  Morris.     Pp.  159-251,  plate  21.  March,  1907.      .75 

12.  Biological  Studies  on  Corymorpha.    II.  The  Development  of  C.  Palma 

from  the  Egg.  By  Harry  Beal  Torrey.  Pp.  253-298,  33  text  figures. 
June,  1907  , .60 

13.  (XVII)  Dinoflagellata  of  the  San  Diego  Region,    in.  Descriptions  of 

New  Species.  By  Charles  Atwood  Kofoid.  Pp.  299-340,  plates  22-23. 
April,  1907 50 

14.  The  Structure  and  Movements  of  Condylostoma  patens,  by  John  F. 

Bovard.    Pp.  343-368,  21  text  figures.    September,  1907 .25 

Index,  pp.  369-383. 

Vol.  4.  1.  The  Ascidians  Collected  by  the  United  States  Fisheries  Bureau  steamer 
Albatross  on  the  Coast  of  California  during  the  Summer  of  1904,  by 
William  Emerson  Ritter.  Pp.  1-52,  plates  1-3.  October,  1907 .60 

2.  (XVIII)  Behavior  of  the  Starfish  Asterias  forreri  de  Lorriol,  by  H.  S. 

Jennings.    Pp.  53-185,  19  text  figures.    November,  1907 1.00 

3.  (XIX)  The  Early  Life-History  of  Dolichoglossus  pusillus  Ritter,  by  B. 

M.  Davis.     Pp.  187-226,  plates  4-8.    March,  1908 .50 

4.  Notes  on  two  Amphipods  of  the  Genus  Corophium  from  the  Pacific 

Coast,  by  J.  Chester  Bradley.     Pp.  227-252,  plates  9-13.    April,  1908.      .30 
6.  (XX)  The  Incrusting  Chilostomatous  Bryozoa  of  the  Western  Coast  of 
North  America,  by  Alice  Robertson.    Pp.  253-344,  plates  14-24,  May, 
1908    1.00 

6.  (XXI)  On  Exuviation,  Autotomy,  and  Regeneration  in  Ceratium,  by 

Charles  Atwood  Kofoid.    Pp.  345-386,  with  text  figures. 

7.  (XXII)  Notes  on  some  Obscure  Species  of  Ceratium,  by  Charles  Atwood 

Kofoid.     Pp.  387-393. 

Nos.  6  and  7  in  one  cover.    April,  1908 . 60 

Index,  pp.  395-400. 

Vol.  5.    1.  The  Biota  of  the  San  Bernardino  Mountains,  by  Joseph  Grinnell.    Pp. 

1-170,  plates  1-24.    December,  1908  - 2.00 

2.  Birds  and  Mammals  of  the  1907  Alexander  Expedition  to  Southeastern 

Alaska.    Pp.  171-264,  pis.  25-26,  figs.  1-4.    February,  1909 .75 

3.  Three  New  Song  Sparrows  from  California,  by  Joseph  Grinnell.    Pp. 

265-269.    April  9,  1909  - 05 

4.  A  New  Harvest  Mouse  from  Petaluma,  California,  by  Joseph  Dixon. 

Pp.  271-273.    August  14,  1909   05 

5.  A  New  Cowbird  of  the  Genus  Molothrus,  with  a  note  on  the  Probable 

Genetic  Relationships  of  the  North  American  Forms,  by  Joseph 
Grinnell.  Pp.  275-281,  1  text  figure.  December,  1909 05 

6.  Two  New  Rodents  from  Nevada,  by  Walter  P.  Taylor.     Pp.  283-302, 

plates  27-29. 

7.  A  Northern  Coast  Form  of  the  Calif  ornia  Gray  Fox,  by  Joseph  Dixon. 

Pp.  303-305. 

Nos.  6  and  7  in  one  cover.    February,  1910 20 


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Marine  Biological  Association  of  San  Diego. 


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